The present invention relates to a delivery container for storing a liquid such as a chemical liquid, a gel-like flowable liquid, or the like and discharging the liquid based on a pumping action.
One known a delivery container for discharging a liquid such as a chemical liquid, a gel-like flowable liquid, or the like is disclosed in Japanese laid-open patent publication No. 5-319466. The disclosed conventional delivery container has a pump disposed in an upper portion thereof for drawing up a liquid from within a chamber in the container. The liquid in the container is drawn via a tube extending downwardly from the pump and discharged from a discharge port positioned above the pump.
The disclosed delivery container has check balls disposed as check valves upwardly and downwardly of the pump. When the pump is pushed, a piston in the pump is displaced downwardly to push the liquid filled in the pump. The lower check ball closes its port and the upper check ball opens its port, allowing the liquid to be discharged from the pump out of the discharge port. When the pump is released of the push, the piston is displaced upwardly under the bias of a spring. The upper check ball closes its port and the lower check ball opens its port, filling the pump with the liquid supplied from the chamber in the container.
The conventional delivery container is relatively complex in structure because of the plural check valves employed for discharging the liquid from the container. For discharging the liquid from the container, the container needs to perform two different actions, i.e., an action to draw the liquid from the chamber into the pump and an action to discharge the liquid from the pump. In each of these actions, the check valves have to operate normally to perform their intended functions. Accordingly, the pump is required to be machined and assembled with high accuracy, and hence is difficult to manufacture. Because the check valves of the conventional delivery container are of a complex construction, the amount of the liquid that is charged in one cycle from the container tends to vary if the check valves suffer a slight error in their operation.
It is necessary to prevent a negative pressure from being developed in the interior of the container because such a negative pressure would make it difficult for the pump to draw in the liquid from the chamber based on a pumping action. The solution employed in the delivery container disclosed in Japanese laid-open patent publication No. 5-319466 is a free piston that slides downwardly in the container as the amount of liquid in the container is reduced, thus preventing a negative pressure from being developed in the container. The free piston and ancillary members make the container structurally complex. Another possible approach to preventing a negative pressure from being developed in the container would be to introduce external air into the container. However, the external air thus introduced would possibly allow microorganisms to find their way into the container, contaminating the liquid in the container.
It is an object of the present invention to provide a delivery container which is of a relatively simple structure and is capable of discharging a metered amount of liquid reliable in each cycle of operation.
To achieve the above object, there is provided in accordance with the present invention a delivery container having a bottomed cylindrical casing for storing a liquid therein, and a cap vertically movably mounted on an upper end of the casing and having a discharge port for discharging the liquid from the casing, the cap being normally biased to move upwardly away from the casing by a spring and movable downwardly toward the casing for discharging the liquid from the casing through the discharge port. The delivery container also has a cylinder disposed in a lower portion of the casing and having an axis extending vertically, a piston vertically slidably disposed in the cylinder and having a communication hole vertically extending therethrough, a hollow shaft having an end connected to the communication hole of the piston and an opposite end connected to the discharge port of the cap, and a check valve disposed in a passage extending from the communication hole via the shaft to the discharge port, for passing the liquid flowing from below the piston and blocking the liquid flowing from above the piston, the cylinder having a flow passageway for providing fluid communication between the interior of the cylinder and the interior of the casing when the piston is positioned upwardly in the cylinder, and blocking fluid communication between the interior of the piston and the interior of the casing when the piston is positioned downwardly in the cylinder.
With the delivery container thus constructed, the cylinder is mounted in the lower portion of the casing, and the flow passageway provides fluid communication between the interior of the piston and the interior of the casing when the piston is positioned downwardly in the cylinder. Therefore, the cylinder is filled with the liquid by gravity from the flow passageway. It is thus not necessary for the cylinder to draw up the liquid as is the case with the conventional delivery container.
When the piston is pushed downwardly, the piston closes the flow passageway, and the liquid in the cylinder flows through the communication hole of the piston, the check valve, and the shaft, and is discharged from the discharge port. Since the piston closes the flow passageway when the liquid is discharged, any other valve mechanisms such as check balls are not required, and hence the mechanism for discharging the liquid is simplified. Because the cylinder is filled with the liquid by gravity at all times, the quantity of the liquid that is discharged is determined by the distance that the piston moves after the piston has closed the flow passageway. As the quantity of the liquid that is discharged from the delivery container is not governed by how good or bad the operation of a conventional valve mechanism is, the quantity of the liquid that is discharged from the delivery container is maintained at a constant level.
When the piston is pushed upwardly under the bias of the spring, the check valve prevents the liquid pushed out of the cylinder from flowing back into the cylinder. The check valve may be simplified in structure as it does not affect the amount of the liquid that is discharged.
If the casing is of a sealed structure, then a negative pressure is developed in the casing when the liquid is discharged from the discharge port. Nevertheless, the liquid can reliably be discharged because the cylinder is filled with the liquid by gravity. The delivery container according to the present invention is of a relatively simple structure as it does not have a free piston slidable in the casing, unlike the conventional delivery container. The sealed casing is protected against the entry of microorganisms into the liquid held in the casing.
The flow passageway preferably comprises a slot defined in the cylinder and extending downwardly from an upper portion of the cylinder across the range in which the piston is slidable, for providing fluid communication between the interior of the cylinder and the interior of the casing, whereby the liquid can be discharged in a quantity determined by the length of the slot. When the piston is depressed over the slot in the cylinder, the liquid flows back from the cylinder into the casing, and is not discharged from the discharge port. When the piston is depressed past the slot in the cylinder, the liquid is discharged from the discharge port. Therefore, if the slot is shorter, the amount of the liquid pushed out by the piston is larger, and if the slot is longer, the amount of the liquid pushed out by the piston is smaller. Since the amount of the liquid discharged from the delivery container can easily be adjusted by the length of the slot, it is easy to change the discharged amount of the liquid depending on the application of the delivery container.
Preferably, the piston and the shaft are integrally coupled substantially linearly to each other, the shaft having a portion projecting upwardly from the casing with the piston mounted in the cylinder. Because the cylinder is positioned in the lower portion of the casing, it would be difficult to install the piston alone in the cylinder. However, as the piston and the shaft are integrally coupled substantially linearly to each other and the shaft has a portion projecting upwardly from the casing with the piston mounted in the cylinder, the piston can be installed in the cylinder by holding the shaft. Thus, it is easy to carry out the process of installing the piston in the cylinder.
The casing preferably has a first tube surrounding the projecting portion of the shaft and extending vertically toward the cap, and the cap having a second tube extending vertically toward the casing and held in slidably fitting relationship to the first tube, the first tube having a first engaging lip projecting from a distal end thereof laterally toward the second tube, and the second tube having a second engaging lip projecting from a distal end thereof laterally toward the first tube, the arrangement being such that when the cap is positioned upwardly, the first engaging lip and the second engaging lip engage each other to retain the cap on the casing.
Since the first tube and the second tube are held in slidably fitting engagement with each other, no dust and dirt enters from the exterior into the space that is surrounded by the first tube and the second tube. In addition, because the portion of the shaft that projects from the casing is positioned in the space surrounded by the first tube and the second tube, no dust and dirt enters the casing upon sliding movement of the shaft relative to the casing when the shaft is vertically moved in response to vertical movement of the cap.